User guide

API reference



Postmark helps deliver and track application email. In a nutshell, the service replaces SMTP (or Sendmail) with a far more reliable, scalable and care-free environment. In addition, you can track statistics such as number of emails sent or processed, opens, bounces and spam complaints.

Things you should know

  • Postmark separates emails by Message Streams. Transactional Message Streams are for one to one emails triggered by a user action like a welcome email, password reset, or order confirmation. Newsletters, announcements, or any other bulk email can be sent through Broadcast Message Streams. If you’re uncertain if your email qualifies as Transactional or Broadcast, you can always contact support and we’ll review your usage.
  • A confirmed email address is required to start sending. Before you can start sending emails, you will need to verify the email address you send from in our Signatures section.
  • Maximum email size is 10 MB. This includes email content, headers, and attachments. You will receive an error if your emails are too large.
  • Postmark will only accept attachments with specific file types, so please review our list of accepted file types. We also support inline image embedding.
  • The maximum number of recipients for each email is 50, including all To, CC, and BCC recipients. Each recipient counts as a single Postmark email or a single Postmark credit for older accounts.

Get started


Get up and running with an existing Postmark library. This is the fastest way to start sending email with Postmark without having to write your own code.

User guide

User guides provide a detailed walk through on accomplishing specific tasks with Postmark. We recommend this if you’re just getting started.